Peer to peer Internet telephony challenges, status and trend Kundan Singh Oct 2010 Peer-to-peer (P2P) systems inherently have high scalability, robustness and fault tolerance because there is no central point of failure and the network self-organizes itself. Skype is a popular and dominant example of P2P VoIP. The IETF P2P-SIP working group was formed to explore a P2P architecture for SIP-based telephony and beyond. Traversal through NATs and firewalls is a major challenge in getting end-to-end media in a distributed P2P network. Another major problem of P2P VoIP is security against malicious peers.   I will present an overview of P2P VoIP,  the challenges, status and current trend in practice. In particular you will learn the advantages and problems associated with P2P VoIP, comparison of various architectures, design decisions and implementations, and a summary of IETF effort.

What will you learn? What is P2P telephony? How is it implemented? What are the benefits and limitations? What is IETF doing about it?

Problem with servers Server-based Peer-to-peer What is P2P telephony? Problem with servers Server-based Operations cost: maintenance, configuration Central points of catastrophic failures Controlled infrastructure (e.g., DNS) Peer-to-peer Robust: no central dependency Self organizing, no configuration Inherently scalable C S P

Peer-to-peer ≠ cloud computing What is P2P telephony? Peer-to-peer ≠ cloud computing Self management Free resource sharing No central co-ordination … Self management Utility computing Central co-ordination … managed

A brief history Napster initiated P2P file sharing What is P2P telephony? A brief history 1999 Napster initiated P2P file sharing “for every one of you that falls, two shall arise.” Distributed hash tables Chord, CAN, Pastry, Tapestry, Kademlia, … Skype (re-)invented P2P-VoIP Now: 13% international calls, 54 billion minutes Demonstrated P2P-SIP at Columbia University IETF WG formed; several more implementations Adobe added P2P to Flash Player Proprietary, E2E but not quite P2P 2001 2003 2004 2008

PBX, H.320, H.324, RTMP, Asterix/IAX, B2BUA, SBC, … What is P2P telephony? signaling + media PBX, H.320, H.324, RTMP, Asterix/IAX, B2BUA, SBC, … signaling media SIP, H.323, XMPP/Jingle, Gtalk, RTSP, RTMFP, … Skype, P2P-SIP, …

(mostly) unstructured Kazaa based  unstructured What is P2P telephony? File sharing Skype P2P-SIP topology (mostly) unstructured Kazaa based  unstructured structured DHT  efficiency guarantee inter-operability implementation driven proprietary/close needs gateway open protocols + algorithms efficiency caching, delay storage, split-and-store overloaded super-nodes caching useless; bounded load centralized varies login server enrollment service malicious nodes incentive driven proprietary software open problem

What is a DHT? Chord consistent hashing data replication What is P2P telephony? What is a DHT? Key node 8+1 = 9 14 8+2 = 10 8+4 = 12 8+8 = 16 21 8+16=24 32 8+32=40 42 1 8 14 21 32 38 58 47 42 10 24 30 54 38 Chord consistent hashing data replication

How to combine SIP + P2P? SIP-using-P2P P2P-over-SIP How is it implemented? How to combine SIP + P2P? SIP-using-P2P SIP location service P2P-over-SIP + implement P2P network using SIP P2P network SIP-using-P2P P2P SIP proxies P2P-over-SIP Maintenance P2P SIP Lookup Alice 128.59.19.194 INSERT INVITE sip:alice@128.59.19.194 FIND P2P network Alice 128.59.19.194 REGISTER INVITE alice SIP overlay

What are super peers? Use DHT among super-peers How is it implemented? 1 10 24 30 54 38 Use DHT among super-peers

Implementation examples How is it implemented? Implementation examples SIPpeer SIPc + OpenDHT Sipeerior SIPDHT OpenVoIP 39 peers SIP thor P2P-over-SIP SIP-using-P2P Data model Service model Adaptor

What are the challenges? What are the benefits and limitations? What are the challenges? Bootstrap a network Security of stored data and keys Data vs service model NAT and firewall traversal Working with free loaders Getting around malicious peers

When to do P2P? if then most of the peers do not trust each other, AND What are the benefits and limitations? When to do P2P? if most of the peers do not trust each other, AND There is no incentive to help peers then P2P does not evolve naturally to work See http://p2p-sip.blogspot.com/2009/10/security-in-p2p-sip.html

Unstructured P2P (blind-search) Structured P2P (Chord) Scaling What are the benefits and limitations? server-based Unstructured P2P (blind-search) Structured P2P (Chord) Scaling server count  ≈ {server-count} user count  K-degree no limit ≈ 2{node-capacity}* uptime, churn, … Efficiency most efficient #connections  maintain = O((logN)2) Call setup latency one or two steps lookup = O(logN) Security trust provider; boolean connect to trusted nodes only trust (most) super nodes; probabilistic Availability server redundancy (1-(1-R)P); catastrophic failure possible; bulk load no guarantee upper bound; catastrophic failure unlikely * Node capacity of 10 register/s and refresh/call rates of 1/min  more than 16 million peers (super-nodes) in the network

IETF P2P-SIP working group What is IETF doing about it? IETF P2P-SIP working group Includes peer protocol, client protocol, SIP usage, locating resources. Excludes modification to SIP, unique identities, “research”-type, search, multicast, dynamic DNS, … Must use existing tools from other WGs

Proposed architecture What is IETF doing about it? Proposed architecture SIP usage XMPP usage MUST Chord DHT 128-bit keys DTLS and TLS Message transport Storage Topology plugin Forwarding and link management TLS DTLS

REsource LOcation And Discovery What is IETF doing about it? REsource LOcation And Discovery Creating pages of specifications draft-ietf-p2psip-base-10 (154p), plus ICE+STUN +TURN+DTLS (260p), and: draft-ietf-p2psip-sip-05, -diagnostics-04, -self-tuning-02, service-discovery-01 Creating unnecessary complexity No compliant implementation; discourages developers/start ups; real problems are out-of-scope 2010 2009

Summary What is P2P telephony? How is it implemented? Versus client-server, end-to-end, and cloud How is it implemented? P2P-over-SIP, SIP-using-P2P, data vs service, adaptor & proxy, What are the benefits and limitations? Scalability, availability, maintenance, lookup What is IETF doing about it? RELOAD, SIP usage, … Visit http://39peers.net for more